The present invention relates to a nonwoven wipe. More particularly, the present invention relates to a nonwoven wipe having improved grease release.
As used herein, the term "wipe" is meant to include any product which is used to clean, polish, or dry any surface. Wipes are employed domestically and industrially for finishing, clean-up, polishing, drying, and like operations, including clean-up involving hand and face contact. In such uses, a wipe often must absorb water and/or oily materials. Additionally, a wipe employed in food service operations desirably also has the ability to release oils and grease upon application of moderate pressure as by hand wringing or squeezing. The terms "wipe" and "wiper" are used synonymously in the art, although the former term is preferred throughout this specification.
U.S. Pat. No. 4,298,649 to Meitner describes a nonwoven disposable wiper. The wiper results from a combination of meltblown microfiber web laminated to at least one web of interconnected aligned split filaments, such as a fibrillated thermoplastic film or foam. The laminate preferably is pattern bonded under the influence of heat and pressure. The laminate preferably contains an ionic or nonionic surfactant.
U.S. Pat. Nos. 4,307,143 and Re. 31,885 to Meitner disclose a microfiber oil and water wipe. A base material of meltblown synthetic, thermoplastic microfibers is treated with a wetting agent and may be pattern bonded in a configuration to provide strength and abrasion resistance properties while promoting high absorbency for both water and oil.
A clean room wiper is described in U.S. Pat. No. 4,328,279 to Meitner et al. A low linting, low sodium ion content wiper is obtained through the use of a treatment involving a mixture of wetting agents.
U.S. Pat. No. 4,493,868 to Meitner discloses a high bulk bonding pattern and method for materials particularly useful as wipers. A variety of materials apparently can be used, although meltblown and coformed polyolefin nonwoven webs appear to be preferred. The total bond area should not exceed 40 percent.
An oil and grease absorbent rinsable nonwoven fabric is described in U.S. Pat. No. 4,587,154 to Hotchkiss et al. The fabric has the capability to release at least about 60 percent of absorbed oil and grease under stated test conditions. The fabric preferably is a meltblown polypropylene web. The web is treated to contain from about 0.5 to 7.5 percent by weight of one or more of a film-forming composition. The web is pattern bonded, preferably in a pattern which covers up to about 30 percent of the surface area.
U.S. Pat. No. 4,906,513 to Kebbell et al. describes a nonwoven wiper laminate. The wiper is a combination of a relatively high basis weight center layer of meltblown thermoplastic microfibers having other fibers or particles mixed therein. On one side of the center layer there is a relatively lightweight layer of continuous filament thermoplastic fibers of larger diameter. On the other side there is a lightweight meltblown microfiber layer. All components are treated with a surfactant for wettability, and the combination is preferably bonded by a patterned application of heat and pressure.
In addition to the foregoing, U.S. Pat. No. 4,041,203 to Brock et al. relates to nonwoven fabrics and sterile wrapper materials made by combining layers of meltblown thermoplastic fibers with one or more continuous thermoplastic filament layers. The disclosure recognizes that such materials can be treated for absorbency and used in wiper applications. U.S. Pat. No. 4,196,245 to Kitson et al. relates to a composite nonwoven fabric useful in disposable surgical items and which can comprise one or more meltblown layers loosely bonded to one or more spunbonded layers.
The formation of fibers by meltblowing is well known in the art. See, by way of example, U.S. Pat. Nos. 3,016,599 to Perry, Jr., 3,704,198 to Prentice, 3,755,527 to Keller et al., 3,795,571 to Prentice, 3,811,957 to Buntin, 3,849,241 to Buntin et al., 3,978,185 to Buntin et al., 4,100,324 to Anderson et al., 4,118,531 to Hauser, and 4,663,220 to Wisneski et al. See, also, V. A. Wente, "Superfine Thermoplastic Fibers", Industrial and Engineering Chemistry, Vol. 48, No. 8, pp. 1342-1346 (1956); V. A. Wente et al., "Manufacture of Superfine Organic Fibers", Navy Research Laboratory, Washington, D.C., NRL Report 4364 (111437), dated May 25, 1954, United States Department of Commerce, Office of Technical Services; and Robert R. Buntin and Dwight T. Lohkamp, "Melt Blowing - A One-Step Web Process for New Nonwoven Products", Journal of the Technical Association of the Pulp and Paper Industry, Vol. 56, No.4, pp. 74- 77 (1973). Composite materials including fibers and/or particulates incorporated in a meltblown fiber matrix are described in U.S. Pat. No. 4,100,324 to Anderson et al. A web of blended microfibers and crimped bulky fibers is disclosed in U.S. Pat. No. 4,118,531 to Hauser.
Wipers made from a matrix of meltblown fibers having incorporated therein a mixture of staple fibers including synthetic and cotton fibers are described in U.S. Pat. No. 4,426,417 to Meitner et al. Laminate wiper materials including a meltblown middle layer with or without other fibers mixed therein between spunbonded outer layers are described in U.S. Pat. No. 4,436,780 to Hotchkiss et al. A laminate material useful for wiping applications and including a layer of meltblown fibers having other fibers or particles mixed therein combined with at least one meltblown layer is described in published European Application No. 0205242.
Because many of the wipes described in the foregoing references utilize nonwoven webs prepared from inherently hydrophobic materials, some means of rendering the surfaces of such materials hydrophilic was necessary. The traditional approach has been to spray or coat the web with a surfactant solution during or after its formation. The web then must be dried, and the surfactant which remains on the web is removed upon exposure of the web to aqueous media. Alternatively, a surfactant can be included in the polymer which is to be melt-processed, as disclosed in U.S. Pat. Nos. 3,973,068 and 4,070,218 to R. E. Weber. However, the surfactant must be forced to the surface of the fibers from which the web is formed. This typically is done by heating the web on a series of steam-heated rolls or "hot cans". This process, called "blooming", is expensive and still has the disadvantage of ready removal of the surfactant by aqueous media. Moreover, the surfactant has a tendency to migrate back into the fiber which adversely affects shelf life, particularly at high storage temperatures. In addition, it is not possible to incorporate in the polymer levels of surfactant much above 1 percent by weight because of severe processability problems; surfactant levels at the surface appear to be limited to a maximum of about 0.33 percent by weight. Most importantly, the blooming process results in web shrinkage in the cross-machine direction and a significant loss in web tensile strength.
U.S. Pat. No. 4,578,414 to L. H. Sawyer and G. W. Knight describes wettable olefin polymer fibers. The fibers are formed from a composition comprising a polyolefin resin and one or more defined surface-active agents. The surfaceactive agents are stated to bloom to the fabricated fiber surfaces where at least one of the surface-active agents remains partially embedded in the polymer matrix. The patent further states that the permanence of wettability can be controlled through the composition and concentration of the additive package.
Polysiloxane/polyoxazolineblock copolymersare disclosed in U.S. Pat. No. 4,659,777 to J. S. Riffle and I. Yilgor. The copolymers are stated to be useful as surface-modifying additives for base polymers.
U.S. Pat. No. 4,689,362 to M. Dexter relates to stabilized olefin polymer insulating materials. Briefly, insulating material for electric wire and cable consists of an olefin polymer stabilized against electrical failure resulting from voltage stress by the presence therein of a polydialkylsiloxanepolyoxyalkylene block or graft copolymer.
U.S. Pat. No. 4,698,388 to H. Ohmura et al. describes a method for modifying the surface of a polymer material by means of a block copolymer. The block copolymer consists of a hydrophilic polymer portion formed from a vinyl monomer and a polymer portion which is compatible with the polymer material, also formed from a vinyl monomer.
A stainproof polyester fiber is described by U.S. Pat. No. 4,745,142 to S. Ohwaki et al. The fiber comprises at least one fiber-forming polyester copolymer comprising a backbone polyester polymer and at least one substituent which blocks at least a portion of the terminals of the molecules of the backbone polyester moiety. The substituent consists of a polyoxyalkylene glycol group.
Polymer compositions having a low coefficient of friction are described by U.S. Pat. No. Re. 32,514 to D. J. Steklenski. The compositions comprise a blend of at least 80 percent by weight of a polymer and at least 0.35 percent by weight of a cross-linked silicone polycarbinol.
Canadian Patent No. 1,049,682 describes the inclusion in a thermoplastic polymer of from 0.1 to 10 percent by weight of a carboxy-functional polysiloxane. Suitable thermoplastic polymers include polyolefins. See, also, German Published Patent Application (Offenlegungschrift) No. 2,506,667 [Chem. Abstr., 84:91066z (1976)].
A significant improvement in the alteration of the surface characteristics of fibers and films prepared from thermoplastic polymers is represented by the surface-segregatable, melt-extrudable thermoplastic compositions described in commonly assigned application Ser. No. 07/181,359, entitled SURFACE-SEGREGATABLE, MELT-EXTRUDABLE THERMOPLASTIC COMPOSITION, filed on Apr. 14, 1988 in the names of Ronald S. Nohr and J. Gavin MacDonald, now U.S. Pat. No. 4,923,914, which patent is incorporated herein by reference.
The compositions described in the patent are particularly useful for the formation of nonwoven webs by such meltextrusion processes as meltblowing, coforming, and spunbonding. Upon being melt-extruded, such compositions result in a fiber having a differential, increasing concentration of the additive from the center to the surface thereof, such that the concentration of additive toward the surface of the fiber is greater than the average concentration of additive in the more central region of the fiber and imparts to the surface of the fiber at least one desired characteristic which otherwise would not be present.
When the additive was a siloxane-containing compound and the desired characteristic was water-wettability, however, the resulting nonwoven webs often became less wettable over time and frequently reverted to a nonwettable state. This loss of wettability, or aging, was accelerated when the polymer composition contained titanium dioxide. However, the absence of titanium dioxide did not prevent the aging which typically was complete within a matter of days.
It subsequently was discovered that the foregoing loss of wettability on aging can be avoided by forming the nonwoven web from a surface-segregatable, melt-extrudable thermoplastic composition which comprises at least one thermoplastic polyolefin and at least one additive having the general formula, ##STR2## in which: (A) R.sub.1 -R.sub.9 are independently selected monovalent C.sub.1 -C.sub.3 alkyl groups;
(B) R.sub.10 is hydrogen or a monovalent C.sub.1 -C.sub.3 alkyl group; PA1 (C) m represents an integer of from 1 to about 4; PA1 (D) n represents an integer of from 0 to about 3; PA1 (E) the sum of m and n is in the range of from 1 to about 4; PA1 (F) p represents an integer of from 0 to about 5 PA1 (G) x represents an integer of from 1 to about 10; PA1 (H) y represents an integer of from 0 to about 5; PA1 (I) the ratio of x to y is equal to or greater than 2; PA1 (J) said additive has a molecular weight of from about 350 to about 1,400; and PA1 (K) said additive is present in an amount of from about 0.5 to about 5 percent by weight, based on the amount of thermoplastic polyolefin. PA1 (2) R.sub.10 is hydrogen or a monovalent C.sub.1 -C.sub.3 alkyl group; PA1 (3) m represents an integer of from 1 to about 4; PA1 (4) n represents an integer of from 0 to about 3; PA1 (5) the sum of m and n is in the range of from 1 to about 4; PA1 (6) p represents an integer of from 0 to about 5; PA1 (7) x represents an integer of from 1 to about 10; PA1 (8) y represents an integer of from 0 to about 5; PA1 (9) the ratio of x to y is equal to or greater than 2; PA1 (10) said additive has a molecular weight of from about 350 to about 1,400; and PA1 (11) said additive is present in an amount of from about 0.5 to about 5 percent by weight, based on the amount of thermoplastic polyolefin; and
Such additive and a method for preparing a wettable nonwoven web which remains wettable after its formation for at least two years at ambient temperature are described and claimed in commonly assigned application Ser. No. 07/485,921, entitled SURFACE-SEGREGATABLE COMPOSITIONS AND NONWOVEN WEBS PREPARED THEREFROM, filed Feb. 27, 1990 in the names of Ronald S. Nohr and J. Gavin MacDonald. It now has been discovered that a wipe comprising a nonwoven web prepared in accordance with the teachings of such application has unexpectedly superior grease release.